Python keeps track of all the packages/modules/libraries included by installation, pip or easy_install using sys.path.
When one types import sys, python looks up in paths contained in sys.path and resolves it.
Lets us have look at the value of sys.path
<pre>kracekumar@python-lover:~$ ipython Python 2.7.1+ (r271:86832, Apr 11 2011, 18:05:24) Type "copyright", "credits" or "license" for more information. IPython 0.10.2 -- An enhanced Interactive Python. ? -> Introduction and overview of IPython's features. %quickref -> Quick reference. help -> Python's own help system. object? -> Details about 'object'. ?object also works, ?? prints more. In [1]: import sys In [2]: sys.path Out[2]: ['', '/usr/local/bin', '/usr/local/lib/python2.7/dist-packages/pip-1.0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/greenlet-0.3.1-py2.7-linux-i686.egg', '/usr/local/lib/python2.7/dist-packages/tweepy-1.7.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/mysite-3-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_model_utils-0.6.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/sessionprofile-1.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_openid-2.2.5_openhatch1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/lockfile-0.9.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/html2text-3.02-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_launchpad_bugs-0.3.6-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_otp-1.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/staticgenerator-1.4.1.2_openhatch-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_voting-0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_registration-0.8_alpha_1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/hexagonit.recipe.download-1.5.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_haystack-1.2.4-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/sisynala-0.9.19-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/South-0.7.3.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/pysolr-2.0.14-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/keyring-0.5.0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/mechanize-0.2.5-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_debug_toolbar-0.8.4-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/pygeoip-0.1.3-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_github2-0.1.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_assets-0.2.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/celery-1.0.5-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_authopenid-1.0.1_openhatch2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/invitation-1.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Traits-3.6.0-py2.7-linux-i686.egg', '/usr/local/lib/python2.7/dist-packages/ipython-0.10.2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/virtualenv-1.6.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_twitter-0.6_devel-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask-0.6.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_SQLAlchemy-0.11-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/newsmeme-0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/blinker-1.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/feedparser-5.0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Markdown-2.0.3-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Themes-0.1.2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Babel-0.6-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_OpenID-1.0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Mail-0.6.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Principal-0.2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Cache-0.3.3-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/speaklater-1.2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Babel-0.9.6-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/lamson-1.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_daemon-1.6-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/mock-0.8.0alpha1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages', '/usr/lib/pymodules/python2.7', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages/PIL', '/usr/lib/pymodules/python2.7/gtk-2.0', '/usr/lib/python2.7/dist-packages/gst-0.10', '/usr/lib/python2.7/dist-packages/gtk-2.0', '/usr/lib/pymodules/python2.7/ubuntuone-client', '/usr/lib/pymodules/python2.7/ubuntuone-control-panel', '/usr/lib/pymodules/python2.7/libubuntuone', '/usr/lib/pymodules/python2.7/ubuntuone-storage-protocol', '/usr/lib/python2.7/dist-packages/wx-2.8-gtk2-unicode', '/usr/local/lib/python2.7/dist-packages/ipython-0.10.2-py2.7.egg/IPython/Extensions', u'/home/kracekumar/.ipython']</pre>
Note: Here Ipython is used .
Here sys.path is list , in case custom path is missing, append the list.
<pre>In [3]: sys.path.append(u'/home/kracekumar/codes/python/snippets/custom/') In [4]: sys.path Out[4]: ['', '/usr/local/bin', '/usr/local/lib/python2.7/dist-packages/pip-1.0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/greenlet-0.3.1-py2.7-linux-i686.egg', '/usr/local/lib/python2.7/dist-packages/tweepy-1.7.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/mysite-3-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_model_utils-0.6.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/sessionprofile-1.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_openid-2.2.5_openhatch1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/lockfile-0.9.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/html2text-3.02-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_launchpad_bugs-0.3.6-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_otp-1.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/staticgenerator-1.4.1.2_openhatch-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_voting-0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_registration-0.8_alpha_1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/hexagonit.recipe.download-1.5.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_haystack-1.2.4-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/sisynala-0.9.19-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/South-0.7.3.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/pysolr-2.0.14-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/keyring-0.5.0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/mechanize-0.2.5-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_debug_toolbar-0.8.4-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/pygeoip-0.1.3-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_github2-0.1.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_assets-0.2.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/celery-1.0.5-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/django_authopenid-1.0.1_openhatch2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/invitation-1.0-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Traits-3.6.0-py2.7-linux-i686.egg', '/usr/local/lib/python2.7/dist-packages/ipython-0.10.2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/virtualenv-1.6.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_twitter-0.6_devel-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask-0.6.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_SQLAlchemy-0.11-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/newsmeme-0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/blinker-1.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/feedparser-5.0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Markdown-2.0.3-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Themes-0.1.2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Babel-0.6-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_OpenID-1.0.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Mail-0.6.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Principal-0.2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Flask_Cache-0.3.3-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/speaklater-1.2-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/Babel-0.9.6-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/lamson-1.1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/python_daemon-1.6-py2.7.egg', '/usr/local/lib/python2.7/dist-packages/mock-0.8.0alpha1-py2.7.egg', '/usr/local/lib/python2.7/dist-packages', '/usr/lib/pymodules/python2.7', '/usr/lib/python2.7', '/usr/lib/python2.7/plat-linux2', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages/PIL', '/usr/lib/pymodules/python2.7/gtk-2.0', '/usr/lib/python2.7/dist-packages/gst-0.10', '/usr/lib/python2.7/dist-packages/gtk-2.0', '/usr/lib/pymodules/python2.7/ubuntuone-client', '/usr/lib/pymodules/python2.7/ubuntuone-control-panel', '/usr/lib/pymodules/python2.7/libubuntuone', '/usr/lib/pymodules/python2.7/ubuntuone-storage-protocol', '/usr/lib/python2.7/dist-packages/wx-2.8-gtk2-unicode', '/usr/local/lib/python2.7/dist-packages/ipython-0.10.2-py2.7.egg/IPython/Extensions', u'/home/kracekumar/.ipython', u'/home/kracekumar/codes/python/snippets/custom/']</pre>
Take a look at the last element of the list, newly added path is updated.
<pre>kracekumar@python-lover:~/codes/python/snippets/custom$ ls like.py like.pyc</pre>
My custom path has one python file named like.py.
Note: This is not demo for packaging, in that case package structure is different.
The source code of like.py.
<pre>kracekumar@python-lover:~/codes/python/snippets/custom$ cat like.py like = 'I love india'</pre>
Now try importing the module.
<pre>In [5]: import like In [6]: like.like Out[6]: 'I love india'</pre>
Be careful while handling sys.path.
